Be very carefull using those plugs, for short term use they are fine but over a long time use they can and will burn the tops of the piston.
They are an extremely hot plug and that is the reason they rarely foul, but any serious mechanic will tell you they will be a problem over the long haul. Just a word of caution..........
Airshot
See my posts above. Been using them since about 1986 in the same motor. I'd have to check my log book, but I'd guess about 500+ hours running time.
500 hours in 28 years? 18 hours a year? That motor doesn't even get a chance to warm up!